[PATCH for-next v2] RDMA/rxe: fix regression caused by recent patch

[Bob Pearson <rpearsonhpe@gmail.com>]

The commit referenced below performs additional checking on
devices used for DMA. Specifically it checks that

device->dma_mask != NULL

Rdma_rxe uses this device when pinning MR memory but did not
set the value of dma_mask. In fact rdma_rxe does not perform
any DMA operations so the value is never used but is checked.

This patch gives dma_mask a valid value extracted from the device
backing the ndev used by rxe.

Without this patch rdma_rxe does not function.

N.B. This patch needs to be applied before the recent fix to add back
IB_USER_VERBS_CMD_POST_SEND to uverbs_cmd_mask.

Dennis Dallesandro reported that Parav's similar patch did not apply
cleanly to rxe. This one does to for-next head of tree as of yesterday.

Fixes: f959dcd6ddfd2 ("dma-direct: Fix potential NULL pointer dereference")
Signed-off-by: Bob Pearson <rpearson@hpe.com>
---
 drivers/infiniband/sw/rxe/rxe_verbs.c | 18 ++++++++++++++++--
 1 file changed, 16 insertions(+), 2 deletions(-)

diff --git a/drivers/infiniband/sw/rxe/rxe_verbs.c b/drivers/infiniband/sw/rxe/rxe_verbs.c
index 7652d53af2c1..c857e83323ed 100644
--- a/drivers/infiniband/sw/rxe/rxe_verbs.c
+++ b/drivers/infiniband/sw/rxe/rxe_verbs.c
@@ -1128,19 +1128,32 @@ int rxe_register_device(struct rxe_dev *rxe, const char *ibdev_name)
 	int err;
 	struct ib_device *dev = &rxe->ib_dev;
 	struct crypto_shash *tfm;
+	u64 dma_mask;
 
 	strlcpy(dev->node_desc, "rxe", sizeof(dev->node_desc));
 
 	dev->node_type = RDMA_NODE_IB_CA;
 	dev->phys_port_cnt = 1;
 	dev->num_comp_vectors = num_possible_cpus();
-	dev->dev.parent = rxe_dma_device(rxe);
 	dev->local_dma_lkey = 0;
 	addrconf_addr_eui48((unsigned char *)&dev->node_guid,
 			    rxe->ndev->dev_addr);
 	dev->dev.dma_parms = &rxe->dma_parms;
 	dma_set_max_seg_size(&dev->dev, UINT_MAX);
-	dma_set_coherent_mask(&dev->dev, dma_get_required_mask(&dev->dev));
+
+	/* rdma_rxe never does real DMA but does rely on
+	 * pinning user memory in MRs to avoid page faults
+	 * in responder and completer tasklets. This code
+	 * supplies a valid dma_mask from the underlying
+	 * network device. It is never used but is checked.
+	 */
+	dev->dev.parent = rxe_dma_device(rxe);
+	dma_mask = *(dev->dev.parent->dma_mask);
+	err = dma_coerce_mask_and_coherent(&dev->dev, dma_mask);
+	if (err) {
+		pr_warn("dma_mask not supported\n");
+		return err;
+	}
 
 	dev->uverbs_cmd_mask |= BIT_ULL(IB_USER_VERBS_CMD_REQ_NOTIFY_CQ);
 
-- 
2.27.0